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July 3, 2009

Study outfits king, clapper rails with radio transmitters

Wildlife biologists from the S.C. Department of Natural Resources and the Nemours Wildlife Foundation are working together to study king and clapper rails in the Ashepoo, Combahee, Edisto (ACE) Basin. Little is known about the life history of these birds and they have traditionally received little research attention. The team extensively expanded use of radio-transmitter telemetry more so than previous tracking studies. Data will also be compiled on reproductive biology and habitat vegetation.

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The study, funded by the U.S. Fish &Wildlife Service’s Webless Migratory Game Bird Research Program, will serve as a Master of Science thesis project for graduate student Cathy Ricketts from the University of Georgia.

The team has had great success capturing clapper rails using an airboat, thermal imaging camera, spotlights and dip nets. Forty-two birds have been banded and outfitted with radio-transmitters in the marsh south of U.S. 17 along the Combahee River and Wimbee Creek. King rails have not been captured successfully with the airboat, so live traps are used instead for them. Two king rails were caught in mid-April and outfitted with radio-transmitters. The birds are tracked 5 days per week by homing in on each individual’s radio frequency. A GPS unit is used to mark the location for each bird and these data points are used to identify an individual’s home range. Currently, enough data points (approximately 800 total) have been collected to create home ranges for 47 rails (44 clappers, 3 kings).

Preliminary analysis shows that some clapper rails exhibit large movements across the marsh landscape (one traveled over 4 miles), while others remain in a relatively small area (5-7 acres). One king rail has remained in a small area (<10 acres) while the other has roamed over an area spanning 300 acres. Plans are to continue capturing and tracking rails throughout the remainder of the year to learn more about their seasonal movements.

In order to learn more about the reproductive biology of rails, nest searches were conducted during the spring. A total of 45 clapper rail nests have been found since early April. Of these, 10 have successfully hatched. Rail chicks are quite mobile upon hatching and can leave the nest within a few hours, so nests are visited every day near the hatch date to determine the fate of the eggs. Some eggs have been washed away by high tides and some have become meals for other marsh dwellers.

Later this summer, biologists will collect information about the vegetation within each bird’s home range to help clarify why rails choose one part of the marsh over another. Vegetation data will also be collected at the site of each nest-- which may provide clues as to why some nests are successful and some are not. In the fall, DNA analysis of feathers collected from each bird will be used to determine sex. It is not possible to determine whether a rail is male or female by appearance alone. This information may help to explain the differences observed in the birds’ movements.

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